The present invention relates to tubing and pipe which are required to be highly resistant against stress corrosion cracking particularly when exposed to hydrogen sulfide.
Generally speaking steel is known to include certain ranges for the alloying elements, carbon, manganese, silicon, chromium, vanadium and nitrogen as disclosed for example in German printed patent application No. 31 27 373. Steel of this type is known to have a yield strength between 480 and 650 N/mm.sup.2. This property however presupposes that the completed steel product has been subjected to a particular programm of deformation and thermal treatment. The type of steel is characterized by the fact that upon making tubes from a hollow and particularly prior to a final longitudinal rolling step the hollow tube has to be cooled to a temperature between the so called Ac1 level and somewhere above 500.degree. C. For the final stretch reducing rolling pass the product is reheated to a temperature above Ar3. The resulting product meets the quality requirements in accordance with API specification N80.
It has to be pointed out however that grade N80 steel is not required nor expected to be resistent against hydrogen sulfide and steel of this type is not expected particularly to be used for example for conducting such a fluid. Therefore grade N80 steel is not expected to have a reliable resistance against stress corrosion cracking. Accordingly API has introduced the grade L80 for use in conjunction with acid gas. Grade L80 steel however has certain limits in its technical properties as compared with grade N80 steel and its hardness is limited to a maximum value of HRC22, and it has annealed grain texture (quenching and tempering). The annealing used here is comprised of quench hardening followed by tempering. This final treatment of the product requires a considerable amount of energy and it is also quite time consuming and is, therefore, regarded as a draw back for this particular kind of product.